Change in transverse relaxation rates (R₂) and change in cognition for older African Americans

Despite transverse relaxation rate (R₂) being one of the fundamental contrasts in MRI, most investigations of brain R₂ and cognition have been cross-sectional and conducted in predominantly non-Latino White adults. We investigated the profile of R₂ as related to cognition in 212 older African Americans (~75 years of age) with longitudinal 3T MRI scans and cognitive test data to determine how changes in R₂ are associated with changes in cognition. For each participant, the slopes of global cognitive and five cognitive domain scores were each separately combined with voxel-specific slopes of R₂ in whole brain voxelwise analyses. Participants with less negative rates of R₂ change within left basal ganglia and centrum semiovale, bilateral hippocampal complex and temporal gyri, parietooccipital white matter, as well as posterior cingulate displayed less negative slopes in global cognition. Similar associations were seen for regional R₂ change and episodic memory (most robustly within bilateral hippocampi) as well as semantic memory (left greater than right hemisphere involvement). Results suggest a relatively wide distribution of regional associations between rates of changes in R₂ and changes in global cognition for older African Americans; a profile that became more regionally specific when considering individual cognitive domains. Relative preservation of tissue integrity across grey and white matter, and in key regions associated with specific cognitive domains, is associated with slower cognitive decline for older African Americans. These results may lay the foundation for more directed work to support healthy brain aging in older African Americans.